The present invention relates to a flywheel-type magneto generator. More particularly, the invention relates to a flywheel magneto generator for a rotary engine that includes a single construction, multi-pole rotor and a three-legged stator, with a magnet provided in the center leg of the stator and coils provided on the outer legs of the stator.
Flywheels and magneto ignitions are typically installed in smaller, two-stroke engines, such as lawn mower and weed eater engines. A magneto is a device that produces alternating current for distribution to the spark plugs of an engine. A conventional flywheel magneto generator includes a rotor assembly and a stator assembly. The rotor assembly has a flywheel and a plurality of poles disposed around the peripheral wall of the flywheel. Permanent magnets are secured by bolts to the poles. A stator assembly confronts the permanent magnets on the rotor to generate electrical energy. These systems have been known to result in large eddy current losses with resultant heat generation in the poles. U.S. Pat. No. 5,214,333 depicts such a flywheel generator. U.S. Pat. No. 4,146,806 discloses a magnet that is secured to the rotor by a screw.
In other flywheel magneto generators, a single magnet is mounted on the flywheel and the flux of the magnet is brought out to the working radius of the flywheel by pole shoes that are made of a magnetically conductive material. The stator assembly is typically a U-shaped core that is made of a magnetically conductive material. The ends of the core are positioned close to the path of the poles"" shoes on the flywheel. The magnet on the rotating flywheel produces a magnetic field through a permeability path provided by the stator assembly. One or more coils are wrapped around the core. When the flux passes through the core, a voltage is generated in the coils. This voltage may be stored or used to start an engine. This prior art system was not optimized since flux was generated in the stator assembly only once for each revolution of the flywheel.
Also, prior art systems that utilized magnets on the flywheel also were required to find ways to attach the magnet to the flywheel, keeping in mind that the flywheel had to be balanced in order to operate smoothly. Magnets have been attached by screws, for instance. Proper balancing of the flywheel rotor is difficult and adds complexity to the system. For instance, U.S. Pat. No. 3,947,710 discloses a flywheel magneto generator that has a flywheel with a balance weight, which is used to balance the output shaft to the rotary engine.
In order to overcome some of the problems that existed with mounting magnets on flywheels, the magnet has been mounted on the stator assembly in a fixed position. For instance, U.S. Pat. No. 5,704,338, the disclosure of which is incorporated herein by reference, discloses a flywheel magneto generator that has a U-shaped stator core with a magnet disposed at one end of the U. The rotor assembly includes a reluctor wheel 47 that is formed from a laminated stack of discs that are made of a highly magnetically permeable material. A circular plate of steel is secured to the top surface of the wheel and includes vanes that are bent to produce a flow of cooling air to the engine when the rotor rotates. Other prior art devices are also known.
The prior art did not provide a magneto generator that could provide an output that increased proportionally to increased rotary speed. For instance, it is desirable to obtain an output voltage that linearly increases as the rotary speed of the generator increases. Prior magnetos provided voltage levels that fell off at rotor speeds of over about 1500 rpms. Such devices also did not meet voltage output requirements at all rotational velocities. Output was found to decrease as flywheel velocities increased. This was caused by eddy current losses. Also, the flux signal of these devices was not sinusoidal. Instead, there were null zones during which the flux changed very little with time. This was undesirable.
The present invention provides a flywheel magneto generator, a rotor for a flywheel magneto generator, and a method of generating electrical energy in an engine. In one embodiment, the flywheel magneto generator for an engine includes a rotor, a stator core, a magnet, and at least one coil. The rotor is mounted for axial rotation to an engine output shaft and has a non-ferromagnetic inner portion and at least one magnetically conductive outer portion. The rotor has a periphery defined by a path of rotation of the outer portion. The stator core is disposed adjacent the periphery of the rotor and is operatively associated therewith. The magnet is operatively coupled to the stator core and the coil is associated with the stator core.
The stator core may have at least two legs and two coils. Each of the coils is associated with one of the legs of the stator core.
The stator core may be E-shaped, having a center leg and two outer legs. The magnet may be connected to the center leg of the core and the coil may be associated with an outer leg of the core. The at least one outer portion may be a pole, with a plurality of poles provided around the circumference of the inner portion. Each of the poles is magnetically isolated from the other poles.
The stator core has a width that extends between three of the poles. In addition, the plurality of poles may be spaced relative to one another to define a gap between each pole. In one embodiment, these gaps are substantially equal in size. The magnet has a width that may be substantially equivalent to the width of the gap between the poles.
In one embodiment, the rotor rotates at a selected speed and an output from the stator core is voltage. The relationship between output voltage and the selected speed is linear so that voltage increases at a substantially constant rate as the selected speed increases. In another embodiment or the same embodiment, voltage, which is generated over a given time period at a constant selected speed, increases and decreases in a substantially sinusoidal manner.
The rotor may include a connection point for attachment to an engine output shaft. In addition, the at least one outer portion of the rotor and the stator core may be formed of bonded iron.
In another embodiment of the invention, the flywheel magneto generator includes a rotor and a stator operatively coupled to the rotor. The rotor includes a flywheel center portion having a circumference and a plurality of poles positioned around the circumference of the flywheel center portion, with each pole having a width. A gap is provided between each of the plurality of poles. The stator includes an E-shaped core having two outer legs and a center leg, with a distance provided between the two outer legs. The gap between the poles is substantially equivalent to the width of the magnet, and the width of each pole is substantially equivalent to the distance between the two outer legs of the core.
The rotor is preferably rotatable and the stator is substantially fixed in position relative to a rotational path of the rotor. The ends of the outer legs of the E-shaped core and the magnet are in close proximity to the rotational path of the rotor. The ends of the legs of the E-shaped core may be configured and dimensioned to substantially align with the rotational path of the rotor. The ends of the legs and the magnet may be spaced about one millimeter from the rotational path of the rotor.
At least one coil may be associated with the E-shaped core. Two coils may be provided. One of the two coils may be operatively coupled to one of the outer legs of the E-shaped core and the other coil may be operatively coupled to the other outer leg of the E-shaped core.
In another embodiment, a rotor for a flywheel magneto generator is provided. The rotor includes a substantially disc-shaped, non-ferromagnetic flywheel having an outer circumference. A plurality of poles are positioned around the outer circumference of the flywheel and extend from the flywheel. The poles are spaced relative to one another. The flywheel and poles together form a single substantial disc-shape.
The poles are magnetically conductive and may be evenly spaced around the circumference of the flywheel. A gap may be provided between each pole of the plurality of poles. Eight poles may be provided and the poles are made of bonded iron. The poles are magnetically isolated relative to one another.
The poles may be joined to the flywheel by a number of methods. For instance, the flywheel and poles may be press-fit together. They may be glued together, or they may be integrally molded together.
The invention also relates to a method for generating electrical energy in an engine having an output shaft with a flywheel magneto generator associated with the output shaft. The method includes providing a non-ferromagnetic flywheel having a circumference with a plurality of magnetically conductive poles. The poles are spaced at equal intervals around the circumference of the flywheel. The method also includes providing a stator assembly with one magnet and at least one coil operatively coupled to the assembly. The stator assembly is in close association with the flywheel. The method further includes rotating the flywheel to generate energy through the at least one coil. The method may also include controlling the flow of generated energy to supply power to charge a battery when the engine is operated above a preselected speed.
In one embodiment of the method, the stator assembly is E-shaped and has two outer legs and a center leg. One coil may be wrapped around one of the outer legs and another coil may be wrapped around the other outer leg. A magnet is positioned at the end of the center leg.